Production of formaldehyde

Abstract

The production of formaldehyde by oxidizing dehydrogenation of methanol in the presence of a silver catalyst using air which has been washed with a solution of an alkali metal compound in water and methanol in specific proportions. The product is a disinfectant, tanning agent, reducing agent and a starting material for the production of synthetic resins, adhesives and plastics.

We claim: 
     
       1. A process for the production of formaldehyde by oxidizing dehydrogenation of methanol with air in the presence of a silver catalyst at elevated temperature wherein the reaction is carried out with air which has been scrubbed with an aqueous solution of 4 to 20% by weight of one or more alkali metal compounds selected from the group consisting of an alkali metal hydroxide, carbonate, alkoxide and salt of a weak or polybasic acid, said aqueous solution also containing 0.5 to 4% by weight of methanol. 
     
     
       2. A process as claimed in claim 1 wherein the air is washed with an aqueous solution of from 5 to 12% by weight of an alkali metal compound and of from 0.6 to 3% by weight of methanol. 
     
     
       3. A process as claimed in claim 1 wherein the scrubbing of the air is carried out in a ratio of from 300 to 5000 parts by volume of air per part by volume of aqueous washing solution containing said alkali metal compound or compounds and methanol. 
     
     
       4. A process as claimed in claim 1 wherein the air is scrubbed at a temperature of from 30° to 150° C. 
     
     
       5. A process as claimed in claim 1 wherein the scrubbing of the air is carried out at a temperature of from 60° to 120° C. 
     
     
       6. A process as claimed in claim 1 wherein the scrubbing of the air is carried out with a mixture of alkali, methanol and water having the composition: from 4 to 20% by weight of said alkali metal compound or compounds and from 0.6 to 3% by weight of methanol based on water which mixture is the bottoms in the evaporator column of the formaldehyde production plant, the air being passed direct through the evaporator bottoms. 
     
     
       7. A process as claimed in claim 1 wherein the methanol of said aqueous solution is crude methanol.